SOLA SOUND: Hybrid MKI Tone Bender

I've had a couple of questions about these recently, and out of curiosity I decided to take a closer look.  In 2024, Sola Sound released a few versions of a hybrid MKI, built by Dave Main of D*A*M.

So what is it?  It’s essentially a standard MKI circuit, but with the first two germanium transistors replaced by silicon transistors.  Because silicon devices don’t leak like germanium, a few extra resistors are needed to get things working properly.

As this is an incomplete trace and there are circuit variants - use the info below as a guide only.

That being said, I have breadboarded this with success - transistors matter....  It sounded a lot like the video demo below, and it was easy to tune playing with input and coupling capacitor values.

SOLA SOUND HYBRID MKI LAYOUT

There aren’t many photos available - I couldn't make out a few values, but I got most of it.  You’ll want to experiment on a breadboard and dial things in before committing to solder.

I ended up making a slightly different layout, as I didn't like some of the placment on this one.

The two values that I just could not see anywhere:  R3 & R7.  For R7, start large and scale down, it seems to tame the gain somewhat - it can also assist with noise if this is a problem.   For R3 I tried a couple of different values.  I have 4k7 on the breadboard at the moment.

The cap values that I could not really see are C1 & C2 on the input & C3.  C3 is just a suitable large electrolytic cap, normally a 22u.

I’m currently using 8k2 for R5 with a 50k pot.  Could probably use a 25k pot and skip R6.  

Groke

Note that R9 is actually 2 x 15k resistor in parallel, wich may as well be the stock value of 8k2.  

The Griffin

Some difference with R5 & R6 are visible. 

Brandy Snap

Looks like a 15n input cap with a 4n7 to ground.  1u coupling cap.  Maybe a 1m5 resistor on the output.

SOLA SOUND: Tone Bender MKII SCB

I was a little surprised when someone requested this, as I assumed that I would have already done it given my love of vintage size vero and Tone Benders.   Anyways, here's the short circuitboard version of the MKII Tone Bender.

What's this short circuitboard business?  It's thought to be the transition from the MK1.5 Tone Bender to the MKII - basically same size board, but jam in the extra transistor stage on the front, hence the crowded layout.

SOLA SOUND TONE BENDER MKII (SCB) - VERO LAYOUT

There's also mention of 12k resistors being used instead of 10k in all the usual forums.  There's also another version with the 100ohm limiting resistor before the Attack pot on the board, but seriously, how much do you want to try jamming on the little board.

More Reading

https://fuzzboxes.org/tonebendermkii

https://stompboxes.co.uk/forum/viewtopic.php?t=6381

SOLA SOUND: Tone Bender MK1.75 'El Diablo'

The El Diablo...   A Dave Main creation, part Sola Sound MK1.5 Tone Bender / part Vox Tone Bender - hence the MK1.75 moniker.  And why El Diablo? apart from the colour, this thing sounds mean as hell.

They appeared to use a couple of different transistors for Q2, but the OC75 remains up front - the OC75 definitely provides a sonic signature in a circuit like this.  The version I saw with the OC84 transistor has a small silva-mica cap between the collector and base of Q1 (I couldn't see the value).  

From the Vox: 

• smaller input cap
• smaller Level pot
• a resistor placed between the Attack pot and ground
• resistor values
• OC76 for Q2

From the MK1.5:  

• 10n output cap (although some Vox carried this)
• and of course, the OC75 for Q1 is pretty important

SOLA SOUND MK1.75 'EL DIABLO' TONE BENDER  -  0.15" VERO LAYOUT

So to get something sounding like the video below from pinstripedclips, I needed to use a relatively low gain transistor ~50hfe for Q1 and in some cases the D*A*M dirty hippie mod, often employed to help bias an OC75. 

I added the video below, as this is much closer to what I was getting on the breadboard with most of my transistors.  Also worth noting as mentioned by Phil in the comments, pinstripedclips has a fairly specific set-up, and who knows how that contributes.   

OC84 VERSION

OC76 VERSION

SOLA SOUND / D*A*M: Goldie MKI Tone Bender

Someone mentioned this in the comments recently (thank you ClassicFuzz), so I thought I'd have a look at the photos on Reverb.  

The Goldie is a MKI in a MKII enclosure from March 2022, likely to be inspired by this unit found in Germany - which is an absolute train wreck of work.  

It looks a lot like a MKII board, it even has a cap to ground on the input - a full set of OC82 transistors is also more likely to be seen on a MKII.  That’s about where the differences end - a nice nod to a MKII, but it’s definitely a MKI.

This Goldie should not be confused with the other Goldie, which is a MK1.5 - confusing no?

SOLA SOUND / D*A*M GOLDIE MKI TONE BENDER - 0.15" VERO LAYOUT

Apart from construction, the most obvious difference to a regular MKI is the cap to ground on the base of Q1 (the silver polystyrene cap).  I haven't been able to spot the value anywhere - thought I could vaguely see an n3 on one, meaning that it might be a 3n3 or similar low-value cap.   D*A*M have used a 3n3 on the input of some MKIs in the past, so probably a safe bet that this is the same.  

I also haven't put eyes on the value of the brown box cap, which is most likely 100n (standard value).  Same for the input cap, I'm assuming 10n as a standard value, but you never know.

Below is the version with the extra resistor in parallel with the 470k which would change the biasing of Q2.  It also appears to have a 47k resistor instead of a 56k resistor on the output.  47k vs 56k makes very little difference.  A slight change to the HPF that it forms with the 100n cap, but not much to worry about (34hz vs 28hz respectively).  There's probably a similar range of variance just with normal component tolerances.

MKI TONE BENDER: Phenolic Board Template

I purchased a sheet of phenolic board locally to make some MKI boards, as I didn't want to pay $25 postage on a $3 board from the USA (postage to Australia is often a killer).  I couldn't find a template anywhere, so I reversed one from a product image online - I did make one slight change to the online product, as I didn't like the alignment of the resistors and capacitor on the righthand side.   

I think it's pretty close as a MKI template, even if it's a metric approximation.   I've built a few boards using this, and the spacing does work with 1/2 watt carbon composite resistors.

MKI TONE BENDER - PHENOLIC BOARD DIMENSIONS / TEMPLATE

safety message:  wear breathing protection when cutting board, even if it's just a medical mask.

Link to MKI component table for variants

SOLA SOUND: Goldie MK1.5 Tone Bender

This is one of the more recent Sola Sound MK1.5 Tone Benders built by David Main.  

MK1.5 TONE BENDER:  THE DIRTY HIPPIE MOD - OC75 ONLY

This has two additions to the regular circuit.  A 10n cap to ground on the input and a 47k bias resistor on the base of Q1 to help stabilise the circuit when it's a bit warmer.  Some Goldies have the resistor hidden under the circuit board, but no 10n cap.  Reference by Mr Main here.    MK1.5s without this mod have been referred to as the 'bear fart' MK1.5 because of the biasing issues.  reference here

The 47k resistor on the base of Q1 certainly makes a difference - the tone is the same, it just adds some extra beef.  Where I live in Australia, it's substantially warmer than England, so this mod is very handy.  How much warmer?  It's winter at the moment, and it's 22 degrees Celsius, not a cloud in the sky.

The OC84 version does not need this mod.  Less leakage I guess.

SOLA SOUND "GOLDIE" TONE BENDER MK1.5 VERO LAYOUT

Here's a nice shot care of Reverb showing the cap value to ground on the input.

SOLA SOUND: Tone Bender MK1.5 - Original 0.15" Vero Layout

A bit of a classic - the MK1.5 Tone Bender.  Some great phots and background information here on Fuzzboxes.org and some great video demos below - who better than Ant Macari to talk Tone Benders.

Note that some earlier versions carried a 500k volume pot, instead of 100k resulting in more bass - ultimately bringing it closer to a Fuzz Face.  

One of the main differences to a Fuzz Face is the use of OC75 transistors.  The key to this is that they are very leaky, and will not bias the same way as a regular fuzz face.  Do not try and bias it like a fuzz face with 4.5v on the collector of Q2 - it will be around 7 or 8 volts.   

SOLA SOUND MK1.5 TONE BENDER - ORIGINAL VERO LAYOUT (0.15" / 3.8MM)

Tone Bender MKII - Component Values Table

Nice bit of MKII history on fuzzboxes.org   The MKII might be the most popular of the Tone Benders, although personally I'm split between the MKI & MKIII.

There's also this interesting timeline on the D*AM forum.  Not sure who made it, but it's a handy reference (thanks ClassicFuzz).  

TONE BENDER MKII SCHEMATIC & VALUES

TONE BENDER MKII COMPONENT VALUES TABLE

R7

Apparently, this resistor was used to shave a bit of gain off circuits that were prone to making unpleasant noises when Attack was set to full.   It's said that this was only on some short board Solas, and some Marshall Suapfuzzes.

C6

My experience with this circuit is that if you don't have a cap on the power, it can oscillate/make terrible noises.  

TONE BENDER MKII LEAKAGE & HFE

A lot of talk about this - I'm not going to get into absolutes, but keep in mind that these originally used quite leaky transistors, and there are reports of nice sounding ones with very high hfe. 

  

APPROXIMATE VOLTAGE RANGE

As the heading suggests - these are approximate voltages only.  Results will vary from unit to unit, and if it sounds good to you, then don't stress about some numbers.  

-4.5 to -5 volts is not what you're after on Q3 collector - that's fuzz face territory.

All voltages shown below are negative

Q1

C   8.5

B   0.3 to 0.06

E   0.0

Q2

C   0.13 to 0.32

B   0.07

E   0.0

Q3

C   7.5 to 8.5 

B   0.13 to 0.22

E   0.1

From DIY Stompboxes, Electric Warrior

Battery: -9.67V

Q1 

C -9.02 

B -0.03 

E 0

Q2 

C -0.17 

B -0.08 

E 0

Q3 

C -8.44 

B -0.17 

E -0.11

MKII TONE BENDER TUNING TIP

Tuning tips by Dave Main - if you're using a trimmer in place of the 8k2 resistor.  

You can also do it by ear, which is much more fun. Get the MKII running into a clean amp at a reasonable volume. Set the Level full and the Attack totally off. Roll your guitar's volume control back a wee bit, about 7-8 if you have a Strat. The tone here should be pretty clear and clean, if you can hear some fuzzy artefacts then inch the trimmer over to the left until they disperse. If you then crank the Attack and pull up your guitars volume you'll also have maximum sustain from the unit, that too should give a little play on any temperature fluctuations.

SOLA SOUND: Tone Bender MKII Professional, Black Fish Skin Hybrid, 0.15" Vero Layout

This is a slightly different hybrid MKII than I have previously seen - this is a Sola Sound MKII built by D*A*M, referred to as the Black Fish Skin version by Macari's Music.  The PNP Silicon transistor is a PNP version of a BC109 / BC108.

I couldn't see the value of one resistor on the photos, so a safe bet would be to try something in the usual range for a MKII, and see how it goes - adjust to taste.  The 10k on the base of Q1 might need to be 100k if you use a different transistor, which is normal for a MKII.

SOLA SOUND TONE BENDER MKII PROFESSIONAL - 0.15" VERO LAYOUT

SOLA SOUND: Tone Bender MKI, Tag Board Layouts

I'm sure there are more than a few layouts out there for the Tone Bender MKI on tag board - I'm sure a couple more will not hurt.  

These are based on the Zonk Machine tag board layout, and I'm planning on adding an extra tag or two to adapt it to a D*A*M FZ-673 and FZ-678, which are normally built on vero.  So this is kind of my jumping-off point if you like.

SOLA SOUND TONE BENDER MKI - TAG BOARD LAYOUT

Original

Gary Hurst

SOLA SOUND TONE BENDER MKIV - TAG BOARD LAYOUT

SOLA SOUND: Tone Bender MKIV, Schematic

 

Sola Sound: Tone Bender MKII Professional Hybrid, 0.15" Vero Layout

This hybrid Tone Bender MKII is a more budget conscious offering from Sola Sound (Macari's) via David Main of D*A*M and it uses NPN transistors, which is a bit of a bonus.

SOLA SOUND TONE BENDER MKII PROFESSIONAL SILICON HYBRID - VERO LAYOUT

Watch out for the hard to spot cuts under the 470 ohm and 100 ohm resistors.

SOLA SOUND: Tone Bender MKII Professional, 0.15" Vero

Not strictly my layout, as this is a copy of the original Sola Sound Tone Bender MKII board.  

This is a little different to most MKII schematics, as it has a 10k resistor from base to ground on Q1, and a 47k on the collector of Q2.  I've read that this is best for leaky OC75 transistors (which I have a few of).  The 100k bias resistors were mainly used for OC81s.   

SOLA SOUND TONE BENDER MKII PROFESSIONAL - VERO LAYOUT

I just realised that I had not posted a Sola Sound Tone Bender MKII layout...  I did the Marshall Supa Fuzz earlier, which is kind of same same but the layout caters for larger mojo parts, and even the D*A*M MKII hybrid for a silicon / germanium monster.  For completeness, here's the MKII.

SOLA SOUND TONE BENDER MKII - POINT TO POINT LAYOUT

The mysterious Sola Sound MK1.5 Tone Bender, which is pretty much a Fuzz Face, or a Fuzz Face is a MK1.5 Tone Bender - either way... just don't try and bias it like a Fuzz Face.

You can the find history of the Tone Bender on Kit Rae's Big Muff Page and also on David Main's (D*A*M) Stompbox site  

You could also use this layout for a standard Fuzz Face.  Be sure to add the usual power filtering if you intend to run this off a power supply, as opposed to a 9V battery.   There should be room on the board.  

SOLA SOUND TONE BENDER MK1.5 - POINT TO POINT LAYOUT

SOLA SOUND: Tone Bender MKII Hybrid, Point to Point Layout

Here's a hybrid Sola Sound Tone Bender MKII using a single germanium transistor at the front, and 2 x silicon at the back - all NPN so it can run off a standard power supply.  

This is a modern bender, made by David Main from D*A*M, for Sola Sound (Macari's Music).  

Apart from running off a normal power supply, AC127 transistors are not super expensive or hard to come by.  

This layout is on my ever growing 'to build' list, so consider it unverified.  I have cross checked the schematic a few times and looked at the gut shots to check part values as much as possible, so it should be fine.

If you prefer vero, then there's a few good layouts out there, including a direct replication of the proper board.  

SOLA SOUND HYBRID TONE BENDER MKII - POINT TO POINT LAYOUT

A slightly smaller point to point layout for the Sola Sound Tone Bender MKIV than the other in my post (for bigger mojo parts).   Of course you can build any Tone Bender MKIII or MKIV from this layout.   

SOLA SOUND TONE BENDER MKIV - COMPACT POINT TO POINT LAYOUT 

NOTE: voltages shown are approximate, and HFE and leakage can be somewhat variable.   From what I have tried, you definitely need a bit of leakage on Q3.  I found breadboarding this circuit more useful than reading opinions on the internet.  

TONE BENDER MKIV - BUILD IN PROGRESS

OC76 for Q3

2 x Micro 2N2996 germaniums for Q1 & Q2

Soviet GE Diode

ON THE SCOPE

Signal:  440hz sine wave, approx 130mv TRMS

Setting:  Fuzz on full

3.3nf capacitor in tone control, instead of 2.2nf

Tone 50%

Tone full bass

Tone full treble